1. Field of the Invention
The present invention generally relates to wireless communication system, and more particularly, to a method and device for processing Hybrid Automatic Repeat reQuest (HARD) transmission for uplink data in a system supporting multi-subframe scheduling.
2. Description of the Related Art
A Long Term Evolution (LTE) system of the 3rd Generation Partnership Project (3GPP) standardization organization may support two duplex modes, that is, Frequency-Division Duplexing (FDD) and Time-Division Duplexing (TDD).
FIG. 1 is a schematic diagram of subframes.
As shown in FIG. 1, for an FDD system, each radio frame has a length of 10 ms, consisting of 10 subframes each having a length of 1 ms. Each radio frame consists two consecutive time slots, the length of which is 0.5 ms. That is, a kth subframe includes time slots 2kth and (2k+1)th. For a TDD system, each radio frame is equally divided into two half-frames, each 5 ms long. Each half-frame includes 8 time slots with a length of 0.5 ms and 3 special fields, i.e., Downlink Pilot Time Slot (DwPTS), Guard Period (GP) and Uplink Pilot Time Slot (UpPTS). A total length of the three special fields is 1 ms long. Each sub-frame consists of two continuous time slots, i.e., the kth subframe includes time slots 2kth and (2k+1)th. One downlink transmission time interval (TTI) is defined in a subframe.
The TDD system supports 7 different LTE uplink-downlink configurations, as shown in Table 1. In Table 1, D represents a downlink subframe, U represents an uplink sub-frame, and S represents the above special subframe consisting of 3 special fields.
TABLE 1LTE TDD uplink-downlink configurationsswitch-configurationpointsubframe numbernumberperiodicity01234567890 5 msDSUUUDSUUU1 5 msDSUUDDSUUD2 5 msDSUDDDSUDD310 msDSUUUDDDDD410 msDSUUDDDDDD510 msDSUDDDDDDD610 msDSUUUDSUUD
The front n Orthogonal Frequency Division Multiplex (OFDM) symbols of each subframe can be used to transmit downlink control information including a Physical Downlink Control CHannel (PDCCH), a Physical HARQ Indicator CHannel (PHICH) and other control information, where n is equal to 1, 2 or 3; the remaining OFDM symbols can be used to transmit Physical Downlink Shared CHannel (PDSCH) or Enhanced PDCCH (ePDCCH). The resource allocation granularity is a Physical Resource Block (PRB). One PRB contains 12 consecutive subcarriers in frequency and corresponds to a time slot in time. In one subframe, two PRBs respectively located in two slots of the subframe while occupying same subcarriers are referred to as a PRB pair. In each PRB pair, each Resource Element (RE) is the smallest unit of time-frequency resources, i.e., a subcarrier in frequency and an OFDM symbol in time.
In the LTE system, the PDCCH carries Downlink Control Information (DCI) allocating uplink channel resource and downlink channel resource, which can be referred as downlink grant signaling and uplink grant signaling, respectively. Grant signaling of different UEs is independently sent, and Downlink grant signaling and uplink grant signaling are independently sent, respectively. Except for uplink data transmission in TDD UL-DL configuration 0, grant signaling in each downlink subframe schedules downlink or uplink transmission of only one subframe. For uplink data transmission in TDD UL-DL configuration 0, since a number of uplink subframes is greater than that of downlink subframes, thus, using one downlink subframe to simultaneously schedule uplink data transmission of at most two uplink subframes can be supported.
In the existing LTE system, for an uplink grant signaling detected in a downlink subframe n, the uplink grant signaling schedules uplink data transmission in uplink subframe n+k. For the FDD system, a value of k is always 4. For a TDD system, a value of k is dependent on TDD UL-DL configurations, as shown in Table 2. For TDD UL-DL configuration 0, scheduling two subframes simultaneously or only one of the subframes can be further distinguished according to an uplink index of DCI.
TABLE 2Values of k corresponding to different TDD UL-DL configurationsconfigurationdownlink subframe index nnumber012345678904, 76, 74, 76, 716464244344444454677775
In the existing LTE system, uplink data transmission is based on synchronous HARQ. Uplink data retransmission can be triggered based on the PHICH. For PHICH information received in downlink subframe n, the PHICH carries HARQ-ACK information for uplink data transmission in uplink subframe n-k. For the FDD system, a value of k is always 4. For the TDD system, a value of k is dependent on TDD UL-DL configurations, as shown in Table 3. For TDD UL-DL configuration 0, two PHICH resource sets are configured in downlink subframes 0 and 5, respectively, and can trigger uplink data transmissions in different uplink subframes.
TABLE 3Values of k between Physical Uplink Shared Control CHannel (PUSCH)timing and PHICH timing corresponding to different TDD UL-DLconfigurationsconfigurationdownlink subframe index nnumber012345678906, 746, 7414646266366646656664746
Further, for PHICH information received in downlink subframe n, the PHICH schedules uplink data transmission in uplink subframe n+k. For the FDD system, a value of k is always 4. For the TDD system, a value of k is dependent on TDD UL-DL configurations, as shown in Table 4. For TDD UL-DL configuration 0, two PHICH resource sets are configured in downlink subframes 0 and 5, respectively, and can trigger uplink data transmissions in different uplink subframes.
TABLE 4Values of k between PHICH timing and retransmission timingcorresponding to different TDD UL-DL configurationsconfigurationdownlink subframe index nnumber012345678904, 774, 7716464244344444454677775
In the follow-up research on LTE, a multi-subframe scheduling technique has attracted more and more attention. As shown in FIG. 1, for uplink multi-subframe scheduling, an uplink grant signaling of one downlink subframe can schedule uplink data transmission of one or more uplink subframes. Through the multi-subframe scheduling technique, resource overhead of scheduling indicators can be saved. Further, if some special subframe cannot send an uplink scheduling command due to not having enough resources, this will result in an uplink subframe corresponding to the downlink subframe that cannot be scheduled; through the multi-subframe scheduling technique, this problem can also be solved. As a special case, a grant signaling of the multi-subframe scheduling may actually schedule uplink data transmission of only one uplink subframe, and the timing relationship is different from that of the existing LTE system.
In fact, in the existing version of LTE, TDD UL-DL configuration 0 already supports the technique of simultaneously scheduling at most two uplink subframes. However, for the FDD system and TDD UL-DL configurations 1˜6, multi-subframe scheduling is not supported. Thus, if the multi-subframe scheduling technique is used, how to perform an effective synchronous HARQ transmission for uplink data transmission is a problem that needs to be solved.